Air stripper

ABSTRACT

An air stripper includes a vessel, a gas delivery tube to deliver a gas into the vessel and a contaminated liquid inlet that provides a contaminated liquid to the vessel at a rate sufficient to maintain a controlled constant level of process fluid within the vessel. A weir is disposed within the vessel adjacent the gas delivery tube to form a first fluid circulation path between a first weir end and a wall of the vessel and a second fluid circulation path between a second weir end and an upper end of the vessel. During operation, gas introduced through the tube mixes with the process fluid and the combined gas and fluid flow at a high rate with a high degree of turbulence along the first and second circulation paths defined around the weir, thereby promoting vigorous mixing and intimate contact between the gas and the process fluid.

FIELD OF THE DISCLOSURE

The disclosure relates generally to devices for contacting gases andliquids, and more specifically, to air strippers that removecontaminants from liquid streams such as volatile substances fromcontaminated water.

BACKGROUND

Air strippers generally partition volatile compounds found withincontaminated liquids, such as groundwater, between liquid and gas phasesby bringing the liquid phase into intimate contact with a stream of air.Volatile contaminants are removed from the liquid as the air isdischarged from the air stripper.

Partitioning of volatile compounds between gas and liquid phases is amass transfer process that is closely defined by Henry's law. Accordingto Henry's law, the equilibrium concentration of a volatile compound inthe water phase is proportional to the partial pressure of the compoundin the air that is in contact with the water. Absent any of the volatilecompound in the air and given adequate time, migration will proceed fromthe liquid phase into the gas phase until equilibrium is reached. As thetemperature increases at a fixed pressure, the Henry's law constant ofproportionality for a given volatile compound increases, meaning thatthe equilibrium concentration for the compound in the water phasedecreases and the equilibrium concentration in the air phase increases.Thus, higher operating temperatures within air strippers increase boththe rate of migration due to the increase in the Henry's law constant(the driving force for the mass transfer) and the percentage of theoriginal mass of the volatile compound within the liquid that canmigrate to the air stream as the system approaches equilibrium.

Several conventional types of air stripping methods that are commonlyused include, for example, packed towers, diffused aeration, trayaeration, and spray aeration. Of these, packed towers and diffusedaeration are the most common methods. The designs of each of these typesof air strippers include means to create zones where the gas and liquidare brought into intimate contact over a large interfacial surface area.The particular method used to create interfacial surface area affectsthe size of the air stripper and compact designs are generally moredesirable considering the value of floor and air space within industrialfacilities and the negative aesthetic impact of larger units wheninstalled outdoors.

Typical packed tower air strippers include a spray nozzle or weir at thetop of a tower to uniformly distribute contaminated water over a columnof packing, a fan to force air counter current to the water flow, and asump at the bottom of the tower to collect decontaminated water. Thepacked tower type air stripper thus increases the interfacial surfacearea between the water and air by distributing the water as a downwardflowing film on the extended surface of the packing material.Accordingly, packed tower type air strippers generally require regularmaintenance (to clean the contact surfaces) and occasionally becomeclogged with suspended matter that is either carried in with the feedliquid or formed by compounds that precipitate out of the water. Cloggedpassageways in packing can also create conditions that stimulatebiological growth further compounding the problem of clogging. Anadditional drawback to the packed tower type air stripper is that abalance must be struck between the amount of void space in the packedcolumn and the restriction that the packing presents to the flow of airin the gas-liquid contact zone. The void space creates a tortuous paththat forces the gas into intimate contact with the liquid film flowingover the packing. Smaller void space increases the velocity of the gasover the liquid film and enhances turbulence, which favorably affectsthe rate of mass transfer from the liquid to the gas phase. Because afinite amount of void space must be employed and additional space isoccupied by the mass of packing, the volume of the gas-liquid contactzone of a packed tower is larger than the required volume of thegas-liquid contact zone within air strippers where the gas is introduceddirectly into the liquid phase, such as diffused aeration. In typicalpacked columns this additional volume compared to diffused aeration isreflected in increased vertical height. For example, to achieveapproximately 99% efficiency, a typical packed tower type air stripperwould require 15 to 20 feet of conventional packing. This can lead tospace problems in certain situations.

On the other hand, diffused aeration devices, typically in the form ofaeration tanks, are generally fairly low profile devices. In a typicalaeration tank air bubbles are introduced into a tank of contaminatedliquid through a distribution manifold that often includes smallopenings and/or diffuser devices such as screens that are usuallylocated near the bottom of the tank and are designed to disperse the gasas uniformly as a possible throughout the liquid. Baffles and multiplegas distribution units may be used to ensure adequate dispersion of airbubbles and residence time for stripping to occur. Aeration tanks areprone to problems similar to the packed tower type systems in that theopenings in the manifold and/or diffuser devices of an aeration tank maybecome clogged with suspended solids and/or biological growth. Thisproblem is compounded by the fact that maximizing the interfacialsurface area between gas and liquid requires minimizing bubble size(i.e., smaller opening in the manifold and/or diffuser screens).

Other than potential fouling and the need for periodic cleaning,traditional packed tower and diffused aeration type air strippers aregenerally good for remediation of liquids that are contaminated withvolatile or semi-volatile organic compounds. To increase the rate andpercentage of mass transfer of such compounds, the contaminated liquidis often preheated prior to treatment. Accordingly, the energy costs ofsuch systems are quite high.

One variation of a diffused aeration type of air stripper is thesubmerged gas evaporators, also known as submerged gas reactors and/orcombination submerged gas evaporator/reactor systems, in which gas isdispersed within a liquid. U.S. Pat. No. 5,342,482, which is herebyincorporated by reference, discloses a common type of submerged gasevaporator, in which combustion gas is generated and delivered though aninlet pipe to a dispersal unit submerged within the liquid to beevaporated. The dispersal unit includes a number of spaced-apart gasdelivery pipes extending radially outward from the inlet pipe, each ofthe gas delivery pipes having small holes spaced apart at variouslocations on the surface of the gas delivery pipe to disperse thecombustion gas as small bubbles as uniformly as practical across thecross-sectional area of the liquid held within the processing vessel.According to current understanding within the prior art, this designprovides desirable intimate contact between the liquid and thecombustion gas over a large interfacial surface area while alsopromoting thorough agitation of the liquid within the processing vessel.

Because submerged gas evaporators/reactors do not require heatexchangers with solid heated surfaces to raise the operating temperatureof the process, these processors provide a significant advantagecompared to conventional air strippers when contact between a heatedliquid stream and a gas stream is desirable.

Suspended solids that may be carried into the air stripper with thecontaminated fluid and/or particles that may precipitate from the liquidundergoing processing can form deposits on extended surfaces of liquiddistribution devices used in conventional air strippers. Buildup ofdeposits on these extended surfaces and the possible formation of largecrystals of precipitates and/or agglomerates related to solid particlescan block passages within processing equipment such as passages in gasdistribution manifold openings and diffuser devices used in diffusedaeration systems or in the system described in U.S. Pat. No. 5,342,482.Such deposits and blockages reduce the efficiency of the air stripperand necessitate frequent cleaning cycles to avoid sudden unplannedshutdowns of the air stripper.

Additionally, most air stripping systems are prone to problems relatedto carryover of entrained liquid droplets that are swept from the liquidphase into the gas phase as the gas passes over and disengages from theliquid phase. For this reason, most air stripper systems include one ormore devices to minimize entrainment of liquid droplets and/or tocapture entrained liquid droplets (e.g., demisters) while allowing forseparation of the entrained liquid droplets from the exhaust gas. Theneed to mitigate carryover of entrained liquid droplets may be relatedto one or more factors including conformance with environmentalregulations, conformance with health and safety regulations andcontrolling losses of material that might have significant value.

Unlike conventional packed tower and tray type air stripping systemswhere mass is transferred from the liquid being processed to the airstream at locations along extended surfaces within the air stripper,mass transfer within submerged gas and diffused aerationevaporators/reactors takes place at the interfacial surface area betweena discontinuous gas phase dispersed within a continuous liquid phase.Compared to the fixed extended surfaces employed in conventional packedtower and tray type air stripping systems, there are no extended solidsurfaces within submerged gas and diffused aeration processors. Thus,because submerged gas processors and diffused aeration tank airstrippers in general rely on dynamic renewable interfacial surface areathat is constantly being formed between liquid and gas phases, theproblem of deposits forming on extended surfaces is eliminated. Thedynamic interfacial surface area that is constantly renewed by a steadyflow of gas into the liquid phase of submerged gas and diffused aerationtank air strippers allows the air and liquid phases to remain in contactfor a finite period of time before disengaging. This finite period oftime is called the residence time of the gas within the evaporation, orevaporation/reaction zone.

Submerged gas and diffused aeration evaporators/reactors also tend tomitigate the formation of large crystals of compounds that precipitatefrom the liquid phase because dispersing the gas beneath the liquidsurface provides mixing within the evaporation or theevaporation/reaction zone, which is a less desirable environment forcrystal growth than a more quiescent zone. Further, active mixing withinan evaporation or reaction vessel tends to maintain solid particles insuspension and thereby mitigates blockages that are related to settlingand/or agglomeration of suspended solids.

However, mitigation of crystal growth and settlement or agglomeration ofsuspended solids is dependent on the degree of mixing achieved within aparticular submerged gas or diffused aeration evaporator/reactor, andnot all submerged gas or diffused aeration evaporator/reactor designsprovide adequate mixing to prevent large crystal growth and relatedblockages. Therefore, while the dynamic renewable interface feature ofsubmerged gas and diffused aeration evaporators/reactors eliminates thepotential for fouling liquids to coat extended surfaces, conventionalsubmerged gas and diffused aeration evaporators/reactors are stillsubject to potential blockages of small openings in the devices used todisperse gas into liquid.

Direct contact between hot gas and liquid undergoing processing within asubmerged gas evaporator/reactor provides excellent heat transferefficiency. If the residence time of the gas within the liquid isadequate for the gas and liquid temperatures to reach equilibrium, asubmerged gas evaporator/reactor operates at a very high level ofoverall energy efficiency. For example, when hot gas is dispersed in aliquid that is at a lower temperature than the gas and the residencetime is adequate to allow the gas and liquid temperatures to reachequilibrium at the adiabatic saturation temperature for the system, allof the available driving forces to affect mass and heat transfer, andallow chemical and physical changes to proceed to equilibrium stages,will have been consumed within the process. The minimum residence timeto attain equilibrium of gas and liquid temperatures within theevaporation, reaction or combined reaction/evaporation zone of asubmerged gas evaporator/reactor is a function of factors that include,but are not limited to, the temperature differential between the hot gasand liquid, the properties of the gas and liquid phase components, theproperties of the resultant gas-liquid mixture, the net heat absorbed orreleased through any chemical reactions and the extent of interfacialsurface area generated as the hot gas is dispersed into the liquid.

Given a fixed set of values for temperature differential, properties ofthe gas and the liquid components, properties of the gas-liquid mixture,heats of reaction and the extent of the interfacial surface area, theresidence time of the gas is a function of factors that include thedifference in specific gravity between the gas and liquid or buoyancyfactor, and other forces that affect the vertical rate of rise of thegas through the liquid phase including the viscosity and surface tensionof the liquid. Additionally, the flow pattern of the liquid includingany mixing action imparted to the liquid such as that created by themeans chosen to disperse the gas within the liquid affect the rate ofgas disengagement from the liquid.

Submerged gas evaporators/reactors may be built in variousconfigurations. One common type of submerged gas evaporator/reactor isthe submerged combustion gas evaporator that generally employs apressurized burner mounted to a gas inlet tube that serves as both acombustion chamber and as a conduit to direct the combustion gas to adispersion system located beneath the surface of liquid held within anevaporation vessel. The pressurized burner may be fired by anycombination of conventional liquid or gaseous fuels such as natural gas,oil or propane; any combination of non-conventional gaseous or liquidfuels such as biogas (e.g., landfill gas) or residual oil; or anycombination of conventional and non-conventional fuels.

Other types of submerged gas evaporators/reactors include hot gasevaporators where hot gas is either injected under pressure or drawn byan induced pressure drop through a dispersion system located beneath thesurface of liquid held within an evaporation vessel. While hot gasevaporators may utilize combustion gas such as hot gas from the exhauststacks of combustion processes, gases other than combustion gases ormixtures of combustion gases and other gases may be employed as desiredto suit the needs of a particular evaporation process. Thus, waste heatin the form of hot gas produced in reciprocating engines, turbines,boilers or flare stacks may be used within hot gas evaporators. In otherforms, hot gas evaporators may be configured to utilize specific gasesor mixtures of gases that are desirable for a particular process such asair, carbon dioxide or nitrogen that are indirectly heated within heatexchangers prior to being injected into or drawn through the liquidcontained within an evaporation vessel.

Regardless of the type of submerged gas evaporator/reactor or the sourceof the gas used within the submerged gas evaporator/reactor, in orderfor the process to continuously perform effectively, reliably andefficiently, the design of the submerged gas evaporator/reactor mustinclude provisions for efficient heat and mass transfer between gas andliquid phases, control of entrained liquid droplets within the exhaustgas, mitigating the formation of large crystals or agglomerates ofparticles and maintaining the mixture of solids and liquids within thesubmerged gas evaporator/reactor vessel in a homogeneous state toprevent settling of suspended particles carried within the liquid feedand/or precipitated solids formed within the process.

SUMMARY OF THE DISCLOSURE

A simple and efficient air stripper includes a vessel and one or moretubes partially disposed within the vessel, which are adapted totransport a gas into the interior of the vessel. The vessel has a fluidinlet that transports a contaminated liquid into the vessel at a ratethat maintains the liquid inside the vessel at a predetermined level anda fluid outlet that is used to withdraw decontaminated liquid. Thecontaminated liquid may be mixed with process aids (e.g., defoamers) andis treated by the gas within the vessel forming a process fluid withinthe vessel. The vessel includes an exhaust stack to allow gas to flowaway from the vessel. In addition, the vessel includes one or more weirsthat at least partially surround the tube or tubes and are submerged inthe process fluid to create a fluid circulation path formed by the spacebetween each weir, or each weir and the wall surface of the vessel, andthe tubes. In one embodiment, each weir is open at both ends and forms alower circulation gap between a first one of the weir ends and a bottomwall of the vessel and an upper circulation gap between a second one ofthe weir ends and the normal operating level of the process fluid withinthe vessel

During operation, gas introduced through each tube mixes with theprocess fluid within the vessel in a first volume formed by each weir,or each weir and the walls of the vessel, and the tube, and the fluidmixture of gas and process fluid flows at high volume with a high degreeof turbulence along the circulation path defined around the weir,thereby causing a high degree of mixing between the gas and the processfluid and any suspended particles within the liquid. Shear forces withinthis two-phase or three-phase turbulent flow region that result from thehigh density liquid phase overrunning the low density gas phase createextensive interfacial surface area between the gas and the process fluidthat favors minimum residence time for mass and heat transfer betweenthe liquid and gas phases to come to equilibrium when compared toconventional gas dispersion techniques. Still further, vigorous mixingcreated by the turbulent flow hinders the formation of large crystals ofprecipitates within the process fluid and, because the system does notuse small holes or any other small ports to introduce the gas into theprocess liquid, clogging and fouling associated with known submerged gasand diffused aeration evaporators/reactors are significantly reduced orentirely eliminated. Still further, the predominantly horizontal flowdirection of the process fluid and gas mixture over the top of the weirand along the surface of the process fluid within the vessel enables thegas phase to disengage from the process fluid with minimal entrainmentof liquid droplets due to the significantly greater momentum of the muchhigher density liquid that is directed primarily horizontally comparedto the low density gas with a relatively weak but constant verticalmomentum component due to buoyancy.

In addition, a method of remediating a contaminated liquid using asubmerged gas evaporator includes providing the contaminated liquid to avessel at a rate sufficient to maintain a process fluid surface at apredetermined level within the vessel, supplying a gas to the vessel,and turbulently mixing the gas and liquid within the vessel that forcesthe gas and process fluid into intimate contact over a large expanse ofinterfacial surface area within the vessel to thereby transfer heatenergy and mass between the gas and liquid phases of a mixture and/or tootherwise react constituents within the gas and liquid phases of amixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an air stripper constructed inaccordance with the teachings of the disclosure.

FIG. 2 is a cross-sectional view of a second air stripper including abaffle.

FIG. 3 is a cross-sectional view of a third air stripper having atubular shaped weir.

FIG. 4 is a top plan view of the air stripper of FIG. 3.

FIG. 5 is a cross-sectional view of a fourth air stripper connected to asource of waste heat.

FIG. 6 is a cross sectional view of a fifth air stripper having multiplegas tubes and multiple weirs.

FIG. 7 is a cross sectional view of a sixth air stripper having multiplemixing chambers within a single vessel.

DETAILED DESCRIPTION

The performance of air strippers according to the disclosure depends onthe properties of the contaminants to be removed from a contaminatedliquid feed stream, the properties of the contaminated liquid feedstream and the temperature and humidity of a gas mixed with thecontaminated liquid feed stream. Usually, the contaminated liquid feedstream is contaminated water and the contaminants to be removed arevolatile and/or semi-volatile compounds. As with conventional airstrippers the removal efficiency for particular contaminants may beestimated by Henry's law which closely defines how each contaminant willpartition between the liquid and gas phases. The advantages of airstrippers according to the disclosure may be realized by substitutingsuch air strippers for conventional air strippers in most air strippingapplications. Wherever air strippers according to the disclosure areemployed, conventional means may be employed to control the flow of thegas and the flow of contaminated liquid through the air stripper and, ifrequired, to post-treat the liquid and/or gas streams. Likewise, mostother conventional means of controlling air stripping systems to meetthe requirements of a particular application may be employed. Also,multiple air strippers according to the invention may be connected inseries or parallel configurations to meet the air stripping demand of aparticular application.

Referring to FIG. 1, an air stripper 10 includes a blower 20 and a gassupply tube or gas inlet tube 22 that provides gas (e.g., air or otherreadily available and desired gas) under positive pressure, the gasinlet tube 22 having sparge or gas exit ports 24 at or near an end 26thereof. The gas inlet tube 22 is disposed within a vessel 30 having abottom wall 31 and a fluid outlet port 32. A contaminated liquid inletport 34 is disposed in one side of the vessel 30 and enables acontaminated liquid 35 to be provided into the interior of the vessel 30and become part of the liquid mixture, process liquid 90, within vessel30. The contaminated liquid may be, but is not limited to, groundwater,landfill leachate, industrial wastewater or produced water from oil orgas recovery wells, and surface water runoff from land used to raiselivestock or crops. The air stripper of FIG. 1. is in the form of asingle-stage air stripper operating in a back-mix mode. Back-mix modemeans that a combination of all three of the following factors areoccurring simultaneously: 1) the continuous addition and mixing ofcontaminated feed liquid 35 and any process aids that might be employedthrough inlet port 34 into the process liquid 90 within vessel 30, alongwith; 2) continuous recirculating flow of the process liquid 90 throughgaps 36 and 37 and; 3) the continuous withdrawal of process fluidthrough outlet port 32 as decontaminated liquid. Thus, the back-mix moderelies on continuous thorough mixing of the contaminated liquid 35 feedand any process aids that might be used with the liquid mixture denotedas process liquid 90 within vessel 30 in combination with many passes ofthe process liquid 90 through the air-liquid contact zone within vessel30 in order to maintain desirable (low) levels of contaminants in theprocess liquid 90 that is withdrawn through outlet port 32 asdecontaminated liquid. However, because the feed of contaminated liquidis into the process liquid 90 is continuous, in the back-mix mode thelevel of contaminants in the decontaminated liquid will always beslightly elevated from the levels that might be attained if one or moreair stripping units connected in series were employed in a manner suchthat the last stage air stripper has no direct hydraulic communicationwith the contaminated liquid inlet port 34. While the back-mix modedesign is adequate to attain the desired level of decontamination of theliquid feed 35 in many common air stripper applications, in somedifficult applications a multi-stage air stripper unit as shown in FIG.7 may be more appropriate to achieve the desired result. In reference tothe air stripper of FIG. 1 it is important to note that the processliquid 90 and the decontaminated fluid that is continuously withdrawnfrom outlet port 32, speaking in a practical sense, are identical incomposition and therefore, for the purposes of this description they areconsidered indistinguishable and therefore considered to be one and thesame. Process aids may include, for example defoaming agents, and theseprocess aids may be provided to the interior of the vessel 30 throughcontaminated liquid inlet port 34. A decontaminated liquid outlet port32 shown at the bottom of the vessel enables process liquid 90 to bewithdrawn from the vessel 30. As has been explained for the air stripper10 of FIG. 1 when operating in the continuous back-mix mode, the processfluid 90 is essentially decontaminated liquid and attains desirabledecontaminated levels after a short time in the vessel. Thus, as long asthe rate of decontaminated fluid removal allows an average residencetime of the contaminated liquid in the vessel 30 that is greater thanthe average time to decontaminate the contaminated liquid, the processfluid 90 will be decontaminated fluid. The small amount of contaminatedliquid added to the process fluid 90 and the vigorous mixing in thevessel 30 allow the process fluid 90 to remain at or below the requiredlevels of decontamination.

Additionally, a weir 40, which is illustrated in FIG. 1 as a flat orsolid plate member having a first or lower end 41 and a second or upperend 42, is disposed within the vessel 30 adjacent the gas inlet tube 22.The weir 40 defines and separates two volumes 70 and 71 within thevessel 30. As illustrated in FIG. 1, a gas exit port 60, disposed in thetop of the vessel 30, enables gas to exit from the interior of thevessel 30. Gas removed from the vessel 30 through exit port 60 may bereleased to atmosphere or transferred into an appropriate downstreamtreatment process, such as an activated carbon absorption system (notshown), to remove contaminants. Disposed at or near a junction of thegas exit port 60 and the vessel 30 is a demister 61. The demister 61removes droplets of process fluid that are entrained in the gas phase asthe gas disengages from the liquid phase at the surface 80. The demister61 may be a vane-type demister, a mesh pad-type demister, or anycombination of commercially available demister elements. Further, avane-type demister may be provided having a coalescing filter to improvedemisting performance. The demister 61 may be mounted in any orientationand adapted to a particular vessel 30 including, but not limited to,horizontal and vertical orientations.

In the air stripper of FIG. 1, the blower 20 supplies air through a line51 to the vessel 30. However, an induction fan (FIG. 2) could be used todraw the air into the vessel 30, in which case the pressure within theinterior of vessel 30 would be less than atmospheric, instead of forcingthe gas into the vessel 30 under positive pressure with the blower 20.Process fluid 90 (which is decontaminated) is withdrawn through theoutlet port 32 at a rate that maintains the desired removal efficiencywith respect to volatile pollutant(s) within contaminated liquid. Thecontaminated liquid and any process aids that may be used are suppliedthrough the contaminated liquid inlet port 34 by a pump (not shown inFIG. 1) at a rate that maintains the surface 80 of the process fluid 90within the vessel 30 at a predetermined level, which may be set by auser. A level sensor and control (not shown in FIG. 1) may be used todetermine and control the rate that the contaminated liquid is suppliedthrough the contaminated liquid inlet port 34.

As illustrated in FIG. 1, the weir 40 is mounted within the vessel 30 toform a lower circulation gap 36 between the first end 41 of the weir 40and the bottom wall 31 of the vessel 30 and to form an upper circulationgap 37 between the second end 42 of the weir 40 and the surface 80 (orthe top wall of the vessel 30). As will be understood, the upper end 42of the weir 40 is preferably set to be at or below the surface 80 whenthe process fluid 90 is at rest (i.e., when no gas is being introducedinto the vessel 30 via the gas inlet tube 22). In some situations, itmay be possible to set the upper end 42 of the weir 40 above the at restlevel of the process fluid 90, as long as introduction of the gas viathe gas inlet tube 22 still causes flow over the upper end 42 of theweir 40. In any event, as illustrated in FIG. 1, the weir 40 alsodefines and separates the confined volume or space 70 in which thesparge ports 24 are located from the volume or space 71. If desired, theweir 40 may be mounted to the vessel 30 via welding, bolts or otherfasteners attached to internal side walls of the vessel 30.

During operation, gas from the line 51 is forced to flow under pressureinto and through the gas inlet tube 22 before reaching the sparge orexit ports 24. The gas exits the gas inlet tube 22 through the spargeports 24 into the confined volume 70 formed between the weir 40, thewall of the vessel 30 and the gas inlet tube 22, causing the gas to bedispersed into the continuous liquid phase of the process fluid 90within the vessel 30. Generally speaking, gas exiting from the spargeports 24 mixes with the process fluid 90 within the confined volume 70and causes a high volume flow pattern to develop around the weir 40. Thevelocity of the flow pattern and hence the turbulence associated withthe flow pattern is highest within the confined volume 70 and at thelocations where the process fluid 90 flows through the upper gap 37 andthe lower gap 36 of the weir 40. The turbulence within the confinedvolume 70 significantly enhances dispersion of the gas into the processfluid 90 which, in turn, provides for efficient heat and mass transferbetween the gas and the process fluid 90. In particular, after exitingthe sparge ports 24, the gas is dispersed as a discontinuous gas phaseinto a continuous liquid phase of the process fluid 90 forming agas/process fluid mixture within the confined volume 70. The mass perunit volume of the gas/process fluid mixture within the confined volume70 is significantly less than the average mass per unit volume of themixture of gas and process fluid in the volume 71. Due to this largedifference in mass per unit volume of process fluid 90 compared to thegas, typically in the order of approximately 1000 to 1, the mass perunit volume of the gas/liquid mixture in the confined volume 70 issignificantly less than that of the average gas/liquid mixture in thevolume 71. This large difference in mass per unit volume creates adifference in static hydraulic pressure between the gas/liquid mixturein the confined volume 70 and the gas/liquid mixture within the volume71 at all elevations within the vertical extent of the weir. Thisimbalance in static hydraulic pressure forces the process fluid 90 toflow from the higher pressure region, i.e., the volume 71, to the lowerpressure region, i.e., the confined volume 70, at a rate that overcomesthe impressed static hydraulic pressure imbalance and creates flowupward through the confined volume 70.

Put another way, the dispersion of gas into the process fluid 90 withinthe confined volume 70 at the sparge ports 24 develops a continuous flowpattern that draws process fluid 90 under the bottom edge 41 of the weir40 through the lower circulation gap 36, and causes the mixture of gasand process fluid 90 to move through the confined volume 70 and towardthe surface 80 Near the surface 80, the gas/liquid mixture reaches apoint of balance at which the imbalance of static hydraulic pressure iseliminated. Generally speaking, this point is at or near the uppercirculation gap 37 formed between the second end 42 of the weir 40 andthe surface 80. At this balance point, the force of gravity, whichbecomes the primary outside force acting on the gas/liquid mixture,gradually reduces the vertical momentum of the gas/liquid mixture tonear zero. This reduced vertical momentum, in turn, causes thegas/liquid mixture to flow in a predominantly horizontal direction overthe second end 42 of the weir 40 (through the circulation gap 37 definedat or near the surface 80 of the process fluid 90) and into the volume71.

This flow pattern around the weir 40 affects the dispersion of the gasinto the continuous liquid phase of the process fluid 90 and, inparticular, creates turbulent mixing action throughout the confinedvolume 70 and the volume 71 and within the continuous liquid phase ofthe process fluid 90 while creating a substantially horizontal flowpattern of the gas/liquid mixture formed within confined volume 70 at ornear the surface 80. This horizontal flow pattern significantlymitigates the potential for entrained liquid droplets to be carriedvertically upward along with the dispersed gas phase as the dispersedgas phase rises through the liquid phase due to buoyancy and finallydisengages from the continuous liquid phase of the process fluid 90 atthe surface 80.

Also, the mixing action created by the induced flow of liquid andliquid/gas mixtures within both the confined volume 70 and the volume 71hinders the formation of large crystals of precipitates, which generallyrequires a quiescent environment. Thus, the mixing action selectivelyfavors the production of relatively small particles of precipitateshelps ensure that the suspended particles formed in the air strippingprocess remain in suspension within the liquid phase circulating aroundthe weir 40, which effectively mitigates the formation of blockages andfouling within the air stripper. Likewise, because relatively smallparticles formed through precipitation are readily maintained insuspension, the efficiency of the air stripper is improved overconventional air stripping systems in terms of freedom from clogging andfouling.

In addition, as the circulating process fluid 90 within volume 71approaches the bottom wall 31 of the vessel 30, the process fluid 90 isforced to flow in a predominantly horizontal direction and through thelower gap 36 into the confined volume 70. This predominantly horizontalflow pattern near the bottom wall 31 of the vessel 30 creates a scouringaction at and above the interior surface of the bottom wall 31 whichmaintains particles of solids including precipitates in suspensionwithin the circulating liquid while the air stripper is operating. Thescouring action at and near the bottom wall 31 of the vessel 30 alsoprovides means to re-suspend settled particles whenever the air stripperis re-started after having been shutdown for a period of time sufficientto allow suspended particles to settle on or near the bottom wall 31.

As is known, air stripping is a process that affects transfer ofvolatile compounds from a liquid phase to a gas phase by creatingintimate contact between a flowing stream of gas and the liquid, whichmay be a compound, a solution or slurry. Within an air stripping processthat uses a submerged gas evaporator, heat and mass transfer operationsoccur simultaneously at the interface formed by the dynamic boundariesof the discontinuous gas and continuous liquid phases. Thus, allsubmerged gas evaporator type air strippers include some method todisperse gas within a continuous liquid phase. The system shown in FIG.1 however integrates the functions of dispersing the gas into the liquidphase, providing thorough agitation of the liquid phase, and mitigatingentrainment of liquid droplets with the gas phase as the gas disengagesfrom the liquid. Additionally, the turbulence and mixing that occurswithin the vessel 30 due to the flow pattern created by dispersion ofgas into liquid within the confined volume 70 reduces the formation oflarge crystals of precipitates and/or large agglomerates of smallerparticles within the vessel 30.

FIG. 2 illustrates a second embodiment of an air stripper 110, which isvery similar to the air stripper 10 of FIG. 1 and in which elementsshown in FIG. 2 are assigned reference numbers being exactly 100 greaterthan the corresponding elements of FIG. 1. Unlike the device of FIG. 1,the air stripper 110 includes a baffle or a shield 138 disposed withinthe vessel 130 at a location slightly above or slightly below thesurface 180 and above the second end 142 of the weir 140. The baffle orshield 138 may be shaped and sized to conform generally to thehorizontal cross-sectional area of the confined volume 170.Additionally, if desired, the baffle 138 may be mounted to any of thegas inlet tube 122, the vessel 130 or the weir 140. The baffle 138augments the force of gravity near the balance point by presenting aphysical barrier that abruptly and positively eliminates the verticalcomponents of velocity and hence, momentum, of the gas/liquid mixture,thereby assisting the mixture to flow horizontally outward and over theweir 140 at the upper circulation gap 137. The baffle enhances themitigation of entrained liquid droplets within the gas phase as the gasdisengages from the liquid. Furthermore, the blower 120 (in this case aninduction fan) is disposed on the gas exit port 160 in this embodiment,thus providing gas to the evaporator vessel 130 under negative pressurei.e., via suction.

As will be understood, the weirs 40 and 140 of FIGS. 1 and 2 may begenerally flat plates or may be curved plates that extend across theinterior of the vessel 30 between different, such as opposite, sides ofthe vessel 30. Basically, the weirs 40 and 140 create a barrier withinthe vessel defining and separating the volumes 70 and 71 (and 170 and171). While the weirs 40 and 140 are preferably solid in nature theymay, in some cases, be perforated, for instance, with slots or holes tomodify the flow pattern within the vessel 30 or 130, or to attain aparticular desired mixing result within the volume 71 or 171, whilestill providing a substantial barrier between the volumes 70 and 71 or170 and 171. Additionally, while the weirs 40 and 140 may extend acrossthe vessels 30 and 130 between opposite walls of the vessels 30 and 130,they may be formed into any desired shape so long as a substantialvertical barrier is formed to isolate one volume 70 (or 170) closest tothe gas inlet tube 22 from the volume 71 (or 171) on the opposite sideof the weir 40, 140.

FIG. 3 illustrates a cross-sectional view of another air stripper 210having a weir 240 that extends around a gas inlet tube 222. The airstripper 210 may be a submerged gas evaporator, a submerged gas reactoror a combination submerged gas evaporator/reactor. A blower device (notshown in FIG. 3) delivers approximately 3,500 standard cubic feet perminute (scfm) of gas to the gas inlet tube 222. While the dimensions ofthe air stripper 210 are exemplary only, the ratios between thesedimensions may serve as a guide for those skilled in the art to achievea desirable balance between three desirable process resultsincluding: 1) preventing the formation of large crystals of precipitatesand/or agglomerates of solid particles while maintaining solid particlesas a homogeneous suspension within the process liquid by controlling thedegree of overall mixing within vessel 230; 2) enhancing the rates ofheat and mass transfer and any desirable chemical reactions bycontrolling the turbulence and hence interfacial surface area createdbetween the gas and liquid phases within confined volume 270; and 3)mitigating the potential of entraining liquid droplets in the gas as thegas stream disengages from the liquid phase at the surface 280 bymaintaining a desirable and predominately horizontal velocity componentfor the gas/liquid mixture flowing outward over the second end 242 ofthe weir 240 and along the surface 280 within vessel 230. As illustratedin FIG. 3, the air stripper 210 includes a vessel 230 with a dishedbottom having an interior volume and a vertical gas inlet tube 222 atleast partially disposed within the interior volume of the vessel 230.In this case, the gas inlet tube 222 has a diameter of approximately 20inches and the overall diameter of the vessel 230 is approximately 120inches, but these diameters may be more or less based on the designcapacity and desired result as related to both gas and liquid flow ratesand the type of blower device (not shown in FIG. 3) supplying gas to theair stripper. In this example the weir 240 has a diameter ofapproximately 40 inches with vertical walls approximately 26 inches inlength. Thus, the weir 240 forms an annular confined volume 270 withinvessel 230 between the weir 240 and the gas inlet tube 222 with crosssectional area of approximately 6.54 square feet (ft²) and volume ofapproximately 14.18 cubic feet (ft³). In the embodiment of FIG. 3,twelve sparge ports 224 are disposed near the bottom of the gas inlettube 222. The sparge ports 224 are substantially rectangular in shapeand are, in this example, each approximately 3 inches wide by 7¼ incheshigh or approximately 0.151 ft2 in area for a combined total area ofapproximately 1.81 ft2 for all twelve sparge ports 224. Additionally,the sparge ports 224 of this embodiment are arranged generally parallelto the flow direction of the gas/liquid phase, further reducing thepossibility of the sparge ports becoming clogged.

As will be understood, the gas exits the gas inlet tube 222 through thesparge ports 224 into a confined volume 270 formed between the gas inlettube 222 and a tubular shaped weir 240. In this case, the weir 240 has acircular cross-sectional shape and encircles the lower end of the gasinlet tube 222. Additionally, the weir 240 is located at an elevationwhich creates a lower circulation gap 236 of approximately 4 inchesbetween a first end 241 of the weir 240 and a bottom dished surface 231of the vessel 230. The second end 242 of the weir 240 is located at anelevation below a normal or at rest operating level of the process fluid290 within the vessel 230. Further, a baffle or shield 238 is disposedwithin the vessel 230 approximately 8 inches above the second end 242 ofthe weir 240. The baffle 238 is circular in shape and extends radiallyoutwardly from the gas inlet tube 222. Additionally, the baffle 238 isillustrated as having an outer diameter somewhat greater than the outerdiameter of the weir 240 which, in this case, is approximately 46inches. However, the baffle 238 may have the same, a greater or smallerdiameter than the diameter of the weir 240 if desired. Several supportbrackets 233 are mounted to the bottom surface 231 of the vessel 230 andare attached to the weir 240 near the first end 241 of the weir 240.Additionally, a gas inlet tube stabilizer ring 235 is attached to thesupport brackets 233 and substantially surrounds the bottom end 226 ofthe gas inlet tube 222 to stabilize the gas inlet tube 222 duringoperation.

During operation of the air stripper 210, gas is ejected through thesparge ports 224 into the confined volume 270 between the gas inlet tube222 and the weir 242 creating a mixture of gas and process fluid 290within the confined volume 270 that is significantly reduced in bulkdensity compared to the average bulk density of the fluid located in thevolume 271 outside of the wall of the weir 240. This reduction in bulkdensity of the gas/liquid mixture within confined volume 270 creates animbalance in head pressure at all elevations between the surface 280within vessel 230 and the first end 241 of the weir 240 when comparingthe head pressure within the confined volume 270 and head pressurewithin the volume 271 outside of the wall of the weir 240 at equalelevations within the vertical extent of the weir. The reduced headpressure within the confined volume 270 induces a flow pattern of liquidfrom the higher head pressure regions of volume 271 through thecirculation gap 236 and into the confined volume 270. Once established,this induced flow pattern provides vigorous mixing action both withinthe confined volume 270 and throughout the volume 271 as liquid from thesurface 280 and all locations within the volume 271 is drawn downwardthrough the circulation gap 236 and upward through the confined volume270 where the gas/liquid mixture flows outward over the second end 242of the weir 240 and over the surface 280 confined within the vessel 230.

Within confined volume 270, the induced flow pattern and resultantvigorous mixing action creates significant shearing forces that areprimarily based on the gross difference in specific gravity and hencemomentum vectors between the liquid and gas phases at all points on theinterfacial surface area of the liquid and gas phases. The shearingforces driven by the significant difference in specific gravity betweenthe liquid and gas phases, which is, generally speaking, of a magnitudeof 1000:1 liquid to gas, cause the interfacial surface area between thegas and liquid phases to increase significantly as the average volume ofeach discrete gas region within the mixture becomes smaller and smallerdue to the shearing force of the flowing liquid phase. Thus, as a resultof the induced flow pattern and the associated vigorous mixing withinthe confined area 270, the total interfacial surface area increases asthe gas/liquid mixture flows upward within confined volume 270. Thisincrease in interfacial surface area or total contact area between thegas and liquid phases favors increased rates of heat and mass transferand chemical reactions between constituents of the gas and liquid phasesas the gas/liquid mixture flows upward within confined volume 270 andoutward over the second end 242 of the weir 240.

At the point where gas/liquid mixture flowing upward within confinedvolume 270 reaches the elevation of the surface 280 and having passedbeyond the second edge 242 of the weir 240, the difference in headpressure between the gas/liquid mixture within the confined volume 270and the gas/liquid mixture within volume 271 is eliminated. Absent thedriving force of differential head pressure and the confining effect ofthe wall of the weir 240, gravity and the resultant buoyancy of the gasphase within the liquid phase become the primary outside forcesaffecting the continuing flow patterns of the gas/liquid mixture exitingthe confined space 270. The combination of the force of gravity and thebarrier created by the baffle 238 in the vertical direction eliminatesthe vertical velocity and momentum components of the flowing gas/liquidmixture at or below the elevation of the bottom of the baffle 238 andcauses the velocity and momentum vectors of the flowing gas/liquidmixture to be directed outward through the gap 239 created by the secondend 242 of the weir 240 and the bottom surface of the baffle 238 anddownwards near the surface 280 within the vessel 230 causing thecontinuing flow pattern of the gas/liquid mixture to assume apredominantly horizontal direction. As the gas/liquid mixture flowsoutwards in a predominantly horizontal direction, the horizontalvelocity component continually decreases causing a continual reductionin momentum and a reduction of the resultant shearing forces acting atthe interfacial surface area within the gas/liquid mixture. Thereduction in momentum and resultant shearing forces allows the force ofbuoyancy to become the primary driving force directing the movement ofthe discontinuous gas regions within the gas/liquid mixture, whichcauses discrete and discontinuous regions of gas to coalesce and ascendvertically within the continuous liquid phase. As the ascending gasregions within the gas/liquid mixture reach the surface 280 within thevessel 230, buoyancy causes the discontinuous gas phase to break throughthe surface 280 and to coalesce into a continuous gas phase that isdirected upward within the confines of the vessel 230 and into the gasexit port 260 under the influence of the differential pressure createdby the blower or blowers (not shown in FIG. 3) supplying gas to the airstripper 210.

FIG. 4 is a top plan view of the air stripper 210 of FIG. 3 illustratingthe tubular nature of the weir 240. Specifically, the generally circulargas inlet tube 222 is centrally located and is surrounded by thestabilizer ring 235. In this embodiment, the stabilizer ring 235surrounds the gas inlet tube 222 and essentially restricts anysignificant lateral movement of the gas inlet tube 222 due to surging orvibration such as might occur upon startup of the system. While thestabilizer ring 235 of FIG. 4 is attached to the support brackets 233 attwo locations, more or fewer support brackets 233 may be employedwithout affecting the function of the air stripper 210. The weir 240,which surrounds the gas inlet tube 222 and the stabilizer ring 235, andis disposed co-axially to the gas inlet tube 222 and the stabilizer ring235, is also attached to, and is supported by the support brackets 233.In this embodiment, the confined volume 270 is formed between the weir240 and the gas inlet tube 222 while the second volume 271 is formedbetween the weir 240 and the side walls of the vessel 230. As will beunderstood, in this embodiment, the introduction of the gas from theexit ports 224 of the gas inlet tube 220 causes contaminated liquid toflow in an essentially toroidal pattern around the weir 240.

Some design factors relating to the design of the air stripper 210illustrated in FIGS. 3 and 4 are summarized below and may be useful indesigning larger or smaller air strippers, which may be used asevaporators or as chemical reaction devices or both. The shape of thecross sectional area and length of the gas inlet tube is generally setby the allowable pressure drop, the configuration of the process vessel,and the costs of forming suitable material to match the desired crosssectional area and the characteristics of the blower that is coupled tothe air stripper. However, it is desirable that the gas inlet tube 222provides adequate surface area for openings of the desired shape andsize of the sparge ports which in turn admit the gas to the confinedvolume 271. For a typical air stripper the vertical distance between thetop edge 242 of the weir 240 and the top edge of the sparge ports shouldbe not less than about 6 inches and preferably is at least about 17inches. Selecting the shape and, more particularly, the size of thesparge port 224 openings is a balance between allowable pressure dropand the initial amount of interfacial area created at the point wherethe gas is dispersed into the flowing liquid phase within confinedvolume 271. The open area of the sparge ports 224 is generally moreimportant than the shape, which can be most any configuration including,but not limited to, rectangular, trapezoidal, triangular, round, oval.In general, the open area of the sparge ports 224 should be such thatthe ratio of gas flow to total combined open area of all sparge portsshould at least be in the range of 1,000 to 18,000 acfm per ft²,preferably in the range of 2,000 to 10,000 acfm/ft² and more preferablyin the range of 2,000 to 8,000 acfm/ft2, where acfm is referenced to theoperating temperature within the gas inlet tube. Likewise, the ratio ofthe gas flow to the cross sectional area of the confined volume 270(CSA_(confined volume)) should be at least in the range of 400 to 10,000scfm/ft², preferably in the range of 500 to 4,000 scfm/ft² and morepreferably in the range of 500 to 2,000 scfm/ft². Additionally, theratio of the cross sectional area of the vessel 230 (CSA_(vessel)) tothe cross sectional area of the confined volume 270 is preferably in therange from three to one (3.0:1) to two-hundred to one (200:1), is morepreferably in the range from eight to one (8.0:1) to one-hundred to one(100:1) and is highly preferably in the range of about ten to one (10:1)to fourteen to one (14:1). These ratios are summarized in the tablebelow. Of course, in some circumstances, other ratios for these designcriteria could be used as well or instead of those particularlydescribed herein.

TABLE 1 Preferred Ratios Embodiment Acceptable Range Preferred Rangeacfm per 2,000-8,000 1,000-18,000 2,000-10,000 Total CSA_(sparge ports)acfm/ft² acfm/ft² acfm/ft² scfm per 500-2,000 400-10,000 500-4000CSA_(confined volume) scfm/ft² scfm/ft² scfm/ft² CSA_(vessel) Ratio to10:1-14:1 3.0:1-200:1 8:1-100:1 CSA_(confined volume)

Turning now to FIG. 5, an air stripper in the form of a submerged gasevaporator/reactor 310 is shown which is similar to the submerged gasevaporator of FIG. 1, and in which like components are labeled withnumbers exactly 300 greater than the corresponding elements of FIG. 1.Unlike the device 10 of FIG. 1, the air stripper 310 of FIG. 5 may ormay not include a blower system but, otherwise as shown receives hotgases directly from an external source, which may be for example, aflare stack, a reciprocating engine, a turbine, or other source of wasteheat. The hot gases supplied by the external source may include a widerange of temperature and/or specific components and these hot gases maybe selected by one skilled in the art to achieve any combination of arate and degree of chemical reaction between components in the gas andliquid, a specific rate of evaporation or to strip contaminants from aliquid or create a desirable concentration of the liquid over time.Alternately, in the absence of an appropriate waste heat source, aburner may be coupled directly to the inlet gas tube 322 to supplyheated combustion air directly to the air stripper. By heating thecontaminated liquid undergoing processing, the efficiency in removingcontaminants can be significantly improved.

The embodiment of an air stripper shown in FIG. 6 includes multiple gastubes 522 and multiple weirs 540. The vessel 530 may include more thanone gas tube 522 and/or more than one weir 540 to increase mass transferefficiency without a significant increase in the size of the airstripper 510 or to use a combination of gases, which may or not includeair to treat contaminated liquid.

The embodiment of an air stripper shown in FIG. 7 includes multiple gastubes 822 and multiple weirs 840 within a single vessel 830, like theembodiment shown in FIG. 6. However, the embodiment shown in FIG. 7 isarranged to provide sequential (multi-stage) processing by having aseries of baffles 892 a, 892 b that divide the vessel into threetreatment chambers 894 a, 894 b, 894 c. Of course, more or less thanthree treatment chambers may be used depending on the amount of spaceavailable and the required level of decontamination. Generally, the moretreatment chambers 894 a, 894 b, 894 c, the greater the decontaminationof the process fluid 890. The contaminated fluid enters the vessel 830into the first treatment chamber 894 a. The contaminated fluid mixeswith the process fluid 890 in the first treatment chamber 894 a. Theprocess fluid 890 is then sequentially treated in each subsequenttreatment chamber 894 b, 894 c further reducing contaminant levels ineach treatment chamber 894 a, 894 b, 894 c. The decontaminated processfluid 890 is removed from the last treatment chamber 894 c at its lowestlevel of contamination. The additional decontamination accomplished ineach chamber is due in part to the introduction of fresh gas into eachtreatment chamber 894 a, 894 b, 894 c.

It will be understood that, because the weir and gas dispersionconfigurations within the air strippers illustrated in the embodimentsof FIGS. 1-7 provide for a high degree of mixing, induced turbulent flowand the resultant intimate contact between liquid and gas within theconfined volumes 70, 170, 270, etc., the air strippers of FIGS. 1-7create a large interfacial surface area for the interaction of thecontaminated liquid (and thus the process fluid) and the gas providedvia the gas inlet tube, leading to very efficient heat and mass transferbetween gas and liquid phases and/or high rates of chemical reactionsbetween components within these two phases. Furthermore, the use of theweir and, if desired, the baffle, to cause a predominantly horizontalflow pattern of the gas/liquid mixture at the surface of the processfluid mitigates or eliminates the entrainment of droplets ofcontaminated liquid within the exhaust gas. Still further, the highdegree of turbulent flow within the vessel mitigates or reduces theformation of large crystals or agglomerates and maintains the mixture ofsolids and liquids within the evaporator/reactor vessel in a homogeneousstate to prevent or reduce settling of precipitated solids. This factor,in turn, reduces or eliminates the need to frequently clean the vesseland can be extremely valuable in situations where the contaminatedliquid 35, 135, etc. contains both volatile pollutants and non-volatilepollutants that may be dissolved or suspended in the contaminated liquid35, 135, etc. In such cases the advantages of the invention can be usedto transfer the volatile pollutants to a gas phase while simultaneouslysignificantly reducing the volume of the process fluid 90, 190, etc.through evaporation (concentration of the process fluid 90, 190, etc.).Highly concentrated process fluid 90, 190, etc. may be realized becausethe turbulent mixing action can maintain significant levels of solidparticles within suspension and there are no extended surfaces or smallpassageways or openings within the system to become coated with depositsor clogged.

While several different types air strippers having different weirconfigurations are illustrated herein, it will be understood that theshapes and configurations of the components, including the weirs,baffles, liquid entry ports, liquid discharge ports, gas entry ports andgas discharge ports used in these devices could be varied or altered asdesired. Thus, for example, while the gas inlet tubes are illustrated asbeing circular in cross section, these tubes could be of any desiredcross sectional shape including, for example, square, rectangular, oval,etc. Additionally, while the weirs illustrated herein have been shown asflat plates or as tubular members having a circular cross-sectionalshape, weirs of other shapes or configurations could be used as well,including weirs having a square, rectangular, oval, or other crosssectional shape disposed around a gas inlet tube, weirs being curved,arcuate, or multi-faceted in shape or having one or more walls disposedpartially around a fire or gas inlet tube, etc. Also, the gas entryports shown as rectangular may assume most any shape includingtrapezoidal, triangular, circular, oval, or triangular. Furthermore, theweirs need not be solid surfaces and may be perforated or latticed ifdesired.

Still further, as will be understood, the terms submerged gas reactor,submerged gas evaporator and submerged gas processor have been usedherein to generally describe air strippers as well as other devices. Asa result, any of the air strippers described or illustrated herein maybe used as evaporators or as chemical reaction devices or both.Likewise, the principles described herein may be used on a submergedcombustion gas evaporator or reaction device, e.g., one that combustsfuel in a burner directly coupled to the air stripper to create the gas,or on a non-combustion gas evaporator or reaction device, e.g., one thataccepts gas from a different source. In the later case, the gas may beheated gas from any desired source, such as an output of a reciprocatingengine or a turbine, a process fueled by landfill gas, or any othersource of heated gas, or a non heated source, such as ambient air orother non heated gases. A reciprocating engine or turbine may operate onlandfill gas or on other types of fuel. Of course, generally speaking,the air strippers described herein may be connected to any source ofwaste heat and/or may be connected to or include a combustion device ofany kind that, for example, combusts one or a combination of a biogas, asolid fuel (such as coal, wood, etc.), a liquid fuel (such as petroleum,gasoline, fuel oil, etc.) or a gaseous fuel. Alternatively, the gas usedin the submerged gas evaporator/reactor may be non-heated and may evenbe at the same or a lower temperature than the liquid within the vessel,and may be provided to induce a chemical or physical reaction of somesort such as the formation of a desirable precipitate.

Still further, as will be understood by persons skilled in the art, theair strippers described herein may be operated in continuous, batch orcombined continuous and batch modes. Thus, in one instance the airstripper may be initially charged with a controlled amount ofcontaminated liquid or process fluid and operated in a batch mode. Inthe batch mode, liquid feed is continuously added to the air stripper tomaintain a constant predetermined level within the vessel by replacingany components of the contaminated liquid (or process fluid) that areevaporated or otherwise withdrawn from the vessel as the processproceeds. Once the batch process has reached a predetermined degree ofconcentration, completeness of a chemical reaction, amount or form ofprecipitate, or any combination of these or other desirable attributes,the process may be shutdown and the desirable product of the process maybe withdrawn from the air stripper for use, sale or disposal. Likewise,the air stripper may be initially charged with a controlled amount ofcontaminated liquid (or process fluid) and operated in a continuousmode. In the continuous mode, liquid feed would be continuously added tothe air stripper to maintain a constant predetermined level within thevessel by replacing any components of the contaminated liquid (orprocess fluid) that are evaporated or otherwise withdrawn from thevessel as the process proceeds. Once the fluid undergoing processing hasreached a predetermined degree of concentration, completeness of achemical reaction, amount or form of precipitate, or any combination ofthese or other desirable attributes, withdrawal of process fluid at acontrolled rate from the vessel would be initiated. The controlledwithdrawal of process fluid would be set at an appropriate rate tomaintain a desirable equilibrium between the rate of feed of the liquidand the gas, the rate of evaporation of components from the contaminatedliquid, and one or more selected values that meet the desired attributesof the process fluid. Thus, in the continuous mode, the air stripper mayoperate for an indeterminate length of time as long as there iscontaminate liquid available and the system remains operational. Thecombined continuous and batch mode refers to operation where, forinstance, the amount of available contaminated liquid is in excess ofthat required for a single batch operation, in which case the processmay be operated for relatively short periods in the continuous modeuntil the supply of contaminate liquid is exhausted.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes in the methods and apparatusdisclosed herein may be made without departing from the scope of theinvention, which is defined in the appended claims.

What is claimed is:
 1. A method of remediating a contaminated liquidhaving volatile contaminants in an air stripper having a weir disposedwithin a vessel to define first and second volumes within the vessel anda gas delivery tube extending into the vessel into the first volume, themethod comprising: supplying contaminated liquid to the vessel at a ratesufficient to maintain a process fluid surface level in the vessel abovea first end of the weir and above a second end of the weir when the airstripper is operating; providing a combustion gas through the gasdelivery tube, which is oriented vertically within the vessel, the gasbeing forced downward through the gas delivery tube to an exit below asurface of the contaminated liquid and radially outward through the exitnear an end of the gas delivery tube and into the first volume definedbetween the weir and the gas delivery tube to cause mixing of thecombustion gas and the process fluid within the first volume by creatinga circular flow of process fluid from the first volume around the firstend of the weir into the second volume and from the second volume arounda second end of the weir and into the first volume, the exit beingformed in a gas delivery tube wall, which is oriented parallel to theweir; removing process fluid through a fluid exit port; and removing thecombustion gas through a gas exit port in the vessel.
 2. The method ofclaim 1, further including removing process fluid with suspendedparticulate from the vessel.
 3. The method of claim 1, further includingcombusting a fuel to create the combustion gas.
 4. The method of claim1, wherein the combustion gas or constituents within the combustion gaschemically react with the process fluid or constituents of the processvessel within the vessel.
 5. The method of claim 1, wherein thecombustion gas at least partially evaporates the process fluid.
 6. Themethod of claim 1, wherein the contaminated liquid is industrial wastewater.
 7. The method of claim 1, wherein the contaminated liquid isgroundwater.
 8. The method of claim 1 wherein the contaminated liquid islandfill leachate.
 9. The method of claim 1, wherein the contaminatedliquid is produced water from oil or gas recovery wells.
 10. The methodof claim 1 wherein the contaminated liquid is surface water runoff fromland used to raise livestock or crops.
 11. The method of claim 1,wherein providing the combustion gas through the gas delivery tube toforce the combustion gas through an exit includes forcing the combustiongas through twelve exits.
 12. The method of claim 1, wherein the exit issubstantially rectangular in shape.
 13. The method of claim 1, whereinproviding the combustion gas through the gas delivery tube to force thecombustion gas through an exit includes providing a ratio of combustiongas to the total combined open area of the exit of between 1,000 and18,000 acfm/ft².
 14. The method of claim 1, wherein providing thecombustion gas through the gas delivery tube to force the combustion gasthrough an exit includes providing a ratio of combustion gas tocross-sectional area of the first volume of between 400 and 10,00scfm/ft².
 15. The method of claim 1, wherein providing the combustiongas through the gas delivery tube to force the combustion gas through anexit includes sequentially providing combustion gas to a multi-stagetreatment chamber.
 16. The method of claim 15, wherein providingcombustion gas to a multi-stage treatment chamber includes separatingthe vessel into a series of chambers with a series of baffles.